1. Field of the Invention
The invention relates to systems used for chemical sterilization of medical devices, and more particularly, to systems having multiple chambers used for chemical sterilization of medical devices.
2. Description of the Related Art
Medical instruments have traditionally been sterilized using either heat, such as is provided by steam, or a chemical, in the gas or vapor state. Sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes.
The combination of hydrogen peroxide with a plasma provides certain additional advantages, as disclosed in U.S. Pat. No. 4,643,876, issued Feb. 17, 1987 to Jacobs et al. U.S. Pat. No. 4,756,882, issued Jul. 12, 1988 also to Jacobs et al. discloses the use of hydrogen peroxide vapor, generated from an aqueous solution of hydrogen peroxide, as a precursor of the reactive species generated by a plasma generator. The combination of hydrogen peroxide vapor diffusing into close proximity with the article to be sterilized and plasma acts to sterilize the articles and remove residual hydrogen peroxide. However, effective sterilization of articles having long narrow lumens are very difficult to achieve, since the methods are dependent upon diffusion of the sterilant vapor into close proximity with the article before sterilization can be achieved. Thus, these methods have been found to require high concentration of sterilant, extended exposure time and/or elevated temperatures when used on long, narrow lumens. For example, lumens longer than 27 cm and/or having an internal diameter of less than 0.3 cm have been particularly difficult to sterilize. The sterilization of articles containing long narrow lumens therefore presents a special challenge.
U.S. Pat. No. 4,744,951 to Cummings et al. discloses a two-chambered system which provides hydrogen peroxide in vapor form for use in sterilization processes. The sterilant is initially vaporized in one chamber and then applied to the object to be sanitized in another single sterilizing chamber, thereby producing a concentrated hydrogen peroxide vapor which is relatively more effective. The sterilization processes are designed for furnishing concentrated hydrogen peroxide vapor to interior surfaces of articles having a tortuous or a narrow path. However, the sterilization processes are ineffective at rapidly sterilizing lumened devices, since they depend on the diffusion of the hydrogen peroxide vapor into the lumen to effect sterilization.
U.S. Pat. No. 4,797,255 to Hatanaka et al. discloses a two-chambered sterilization and filling system consisting of a single sterilization chamber adjacent to a germ-free chamber utilized for drying and filling sterilized containers.
U.S. Pat. No. 4,863,688 to Schmidt et al. discloses a sterilization system consisting of a liquid hydrogen peroxide vaporization chamber and an enclosure for sterilization. The enclosure additionally may hold containers wherein the hydrogen peroxide sterilant vapor does not contact the interior of the containers. This system is designed for controlling the exposure to the hydrogen peroxide vapor. The system is not designed for sterilizing a lumen device.
U.S. Pat. No. 4,952,370 to Cummings et al. discloses a sterilization process wherein aqueous hydrogen peroxide vapor is first condensed on the article to be sterilized, and then a source of vacuum is applied to the sterilization chamber to evaporate the water and hydrogen peroxide from the article. This method is suitable to sterilize surfaces, however, it is ineffective at rapidly sterilizing lumened devices, since it too depends on the diffusion of the hydrogen peroxide vapor into the lumen to effect sterilization.
U.S. Pat. No. 4,943,414, entitled "Method for Vapor Sterilization of Articles Having Lumens," and issued to Jacobs et al., discloses a process in which a vessel containing a small amount of a vaporizable liquid sterilant solution is attached to a lumen, and the sterilant vaporizes and flows directly into the lumen of the article as the pressure is reduced during the sterilization cycle. This system has the advantage that the water and hydrogen peroxide vapor are pulled through the lumen by the pressure differential that exists, increasing the sterilization rate for lumens, but it has the disadvantage that the vessel needs to be attached to each lumen to be sterilized.
U.S. Pat. Nos. 4,937,046, 5,118,471 and 5,227,132 to Anderson et al. each disclose a sterilization system which uses ethylene oxide gas for sanitation purposes. The gas is initially in a small first enclosure and thereafter slowly permeates into a second enclosure where the objects to be sterilized are located. A medium is then introduced into the second enclosure to flush out the sterilizing gas into a third enclosure containing the second enclosure. An exhaust system then exhausts the sterilant gas and air from the third enclosure. These systems also have the disadvantage of relying on the diffusion of the sterilant vapor to effect sterilization and hence are not suitable for rapidly sterilizing lumened devices.
U.S. Pat. No. 5,122,344 to Schmoegner discloses a chemical sterilizer system for sterilizing items by vaporizing a liquid chemical sterilant in a sterilizing chamber. Pre-evacuation of the sterilizer chamber enhances the sterilizing activity. Sterilant is injected into the sterilizer chamber from a second prefilled shot chamber. This system also relies upon diffusion of sterilant vapor to effect sterilization and is also not suitable for rapidly sterilizing lumened devices.
U.S. Pat. No. 5,266,275 to Faddis discloses a sterilization system for disinfecting instruments. The sterilization system contains a primary sterilization chamber and a secondary safety chamber. The secondary safety chamber provides for sensing and venting to a destruction chamber any sterilization agent that is released from the primary sterilization chamber. This system, as in other systems, also relies upon diffusion of sterilant vapor to effect sterilization and is also not suitable for rapidly sterilizing lumened devices.
In U.S. Pat. Nos. 5,492,672 and 5,556,607 to Childers et al, there is disclosed a process and apparatus respectively for sterilizing narrow lumens. This process and apparatus uses a multicomponent sterilant vapor and requires successive alternating periods of flow of sterilant vapor and discontinuance of such flow. A complex apparatus is used to accomplish the method. Additionally, the process and apparatus of '672 and '607 require maintaining the pressure in the sterilization chamber at a predetermined subatmospheric pressure.
In U.S. Pat. No. 5,527,508 to Childers et al., a method of enhancing the penetration of low vapor pressure chemical vapor sterilants into the apertures and openings of complex objects is disclosed. The method repeatedly introduces air or an inert gas into the closed sterilization chamber in an amount effective to raise the pressure to a subatmospheric pressure to drive the diffused sterilant vapor further into the article to achieve sterilization. The '508, '672 and '607 Childers inventions are similar in that all three require repeated pulsations of sterilant vapor flow and maintenance of the sterilization chamber pressure at a predetermined subatmospheric pressure.
In U.S. Pat. No. 5,534,221 to Hillebrenner et al., a device and method for sterilizing and storing an endoscope or other lumened medical device is disclosed. The device includes a sealable cassette in which the endoscope or other medical device is placed. The cassette has an input port for receiving a sterilizing agent through a connector, an output port for expelling the sterilizing agent when a vacuum is applied thereto through a connector, and check valves in the input and output ports to open the ports when the connectors are coupled to the ports and to seal the ports when the connectors are removed from the ports such that after the endoscope has been sterilized, it remains sterilized within the cassette until the cassette is opened. The method of the '221 invention involves placing the medical device inside the cassette and coupling the device to either the input or output port of the cassette. The cassette is then placed in an outer oven-like container or warming chamber where the temperature is properly maintained. Connections are made to open the input and output ports on the cassette such that the sterilizing agent may be introduced through a first port to bathe the outside of the medical instrument or other object, such as an endoscope while one end of the hollow object, such as the endoscope, is coupled to the output port where a vacuum is supplied external to the cassette to pull the sterilization agent into the cassette and through the interior passageways of the endoscope. When the sterilization process is completed, the warming chamber is opened and the sterilizing cassette is simply removed from the chamber with the input and output ports being uncoupled from their respective sources. A tight seal is maintained and the object remains in the sterilized interior of the cassette until the cassette is opened or the device is to be used. Thus, the '221 invention is concerned with providing a means whereby a sterilized medical device can be retained within a cassette in which it was sterilized until ready for use, thus avoiding any contamination by exposure to the atmosphere or handling before use. Additionally, in some cases of the '221 invention, wherein the lumen of the device to be sterilized is connected to the output port, particularly wherein the devices have long, narrow lumens, the time to expel the sterilizing agent through the lumen and out of the cassette may be undesirably long. Also, in cases wherein the lumen device is very flexible, lumen collapse may occur, either slowing or preventing vapor exit or causing lumen damage.
U.S. Patents Nos. 5,445,792 and 5,508,009 to Rickloff et al. each disclose a sterilization system essentially equivalent to the system disclosed in Hillebrenner '221.
U.S. Pat. No. 5,443,801 to Langford teaches a transportable cleaning/sterilizing apparatus and a method for inside-outside sterilization of medical/dental instruments. The apparatus avoids the use of heat, pressure, severe agitation, or corrosive chemicals which might damage delicate equipment. This invention uses ozone gas or solution as sterilant. It does not involve the use of sterilant vapor or vaporizing a sterilant solution into vapor, and is not suitable for operations under vacuum because flexible bags or containers are used.
In consideration of the foregoing, no simple, safe, effective method of sterilizing smaller lumens exists in the prior art. Thus, there remains a need for a simple and effective method of vapor sterilization of articles with both long, narrow lumens as well as shorter, wider lumens. Furthermore, there also remains a need for a simple and effective sterilization system with independently operable chambers.